The present invention relates generally to a bone conduction hearing aid device.
It is known that the normal perception of sounds results from the transmission of sound waves to an organ called the cochlea situated in the inner ear. More precisely, the acoustic signals or sound waves are picked up by the outer ear, and then transmitted to the middle-ear through the tympanic membrane in order to be perceived by the cochlea which is immobilized in the skull. As a result, a nerve impulse is generated and transmitted to the brain through the auditory nerve.
The more conventional air propagation hearing aid devices work by amplification of the sound signal, notably by means of a loudspeaker placed in the outer ear canal.
Other hearing aid devices, not as well known, are called bone conduction hearing aids and their function is to excite the cochlea by vibrating the skull. Such devices comprise a transmitter part and a receiver transducer part comprising a vibrating element which is placed either against the skin, usually behind the ear, under a certain pressure, or actually in contact with the bone in the mastoid area.
However, said devices have not proven to be satisfactory. Indeed, the apparatuses using a vibrator placed against the skin require strong pressures in order to be efficient (i.e. to transmit the vibrations through the skin) and consequently, they can only be worn for relatively short periods, in order not to cause pain or in some cases, epidermal lesions. What is more, psychologically, the persons on whom they are fitted dislike them on the whole as they are generally visible and inaesthetic.
In addition, the direct bone conduction devices necessitate a surgical operation in order to be fitted. And furthermore, the use of such devices raises a number of serious problems of maintenance such as charging or replacement of the batteries, reaction of the bone subjected to vibrations, adjustment, replacement in case of breakdowns.